Polyolefins and other polymers are frequently modified in order to improve their rheological and other physical properties. Various chemical agents have been used to carry out such modifications.
One method for modifying polymers, such as polyolefins, is to use molecules that are capable of providing a nitrene reactive group(s) for insertion into Cxe2x80x94H bonds on the polymers. An example of such a class of chemicals are the sulfonyl azides which are disclosed in WO 99/10424 published Mar. 4, 1999, which is hereby incorporated by reference for its teachings regarding azides. When heated to an appropriate reaction temperature, these azides decompose to form nitrene groups that can then insert into Cxe2x80x94H bonds on the polymers. These sulfonyl azides are effective for providing nitrene groups for insertion into the Cxe2x80x94H bonds of styrenic based and polyolefin based polymers.
However, sulfonyl azides and other azides can be shock sensitive. It may be necessary to phlagmatize the azides or to otherwise protect the azides from reaction during the manufacture and processing of the azide and the shipping and handling of the azide. However, the methods that would typically be used to protect chemicals such as azides from reacting can be expensive and may not be compatible with the polymers that are to be modified. Additionally, polymers are often used for packaging food. Therefore, it is important that the addition of the protective agent not prevent the modified polymer from being approved for food packaging applications.
What is desired is a relatively inexpensive and easy manner for phlagmatizing a coupling agent that also does not interfere with the coupling agent or limit the use of the coupling agent for producing modified polymers.
As used herein, the following terms shall have the following meanings:
(a) xe2x80x9cCoupling Agentxe2x80x9d shall mean a chemical compound that contains at least two reactive groups that are each capable of forming a carbene or nitrene group that are capable of inserting into the carbon hydrogen bonds of CH, CH2, or CH3 groups, both aliphatic and/or aromatic, of a polymer chain. The reactive groups together can couple or cross-link polymer chains. It may be necessary to activate a coupling agent with heat, sonic energy, radiation or other chemical activating energy, for the coupling agent to be effective for coupling and/or cross-linking polymers chains.
(b) xe2x80x9cPhlagmatizingxe2x80x9d refers to methods for reducing the shock sensitivity of a chemical or chemical species by mixing or combining the reactive chemical with an inert or less reactive chemical.
(c) xe2x80x9cmolecular meltxe2x80x9d refers to an at least partially amorphous blend, at room temperature, of a coupling agent (modifying agent) and an antioxidant, optionally also containing other polymer additives. Both the coupling agent (modifying agent) and the antioxidant are at least partially contained in the amorphous phase of the blend. Also, preferably the coupling agent (modifying agent) and the antioxidant form a complex where the Raman spectra relating to the groups forming the nitrene groups are shifted compared to the Raman spectra exhibited by the groups forming the nitrene groups of the coupling agent alone.
(d) xe2x80x9cantioxidantxe2x80x9d refers to types or classes of chemical compounds that are capable of being used to minimize the oxidation that can occur during the processing of polymers. The term also includes chemical derivatives of the antioxidants, including hydrocarbyls. The term further includes chemical compounds, as described later in the description of the antioxidant, that when properly combined with the coupling agent (modifying agent) interact with to form a complex which exhibits a modified Raman spectra compared to the coupling agent or modifying agent alone.
(e) xe2x80x9cmodifying agentxe2x80x9d refers to a chemical compound that contains a reactive group capable of forming a carbene or a nitrene group that can react with a polymer chain.
(f) xe2x80x9ctarget polymerxe2x80x9d refers to a polymer that is intended to be modified by the coupling or modifying agent. The target polymer can be any polymer that contains CH, CH2, or CH3 groups, aliphatic or aromatic, of a polymer chain. Preferably, the target polymer can be any polyolefin (including polyethylene) or styrenic based polymer.
(g) xe2x80x9cDSCxe2x80x9d refers to a differential scanning calorimeter or differential scanning calorimetry analysis, depending on the context it is used in. DSC is a method one of ordinary skill in the art is familiar with to determine the crystallinity of a polymer.
(h) xe2x80x9cNitrene groupxe2x80x9d refers to a compound having a structure Rxe2x80x94N, where N is nitrogen capable of reacting with a polymer chain by inserting into the carbon hydrogen bonds of CH, CH2, or CH3 groups, both aliphatic and/or aromatic, of a polymer chain. It is believed that the nitrogen most preferred for inserting into the carbon hydrogen bonds has two lone pairs of electrons. R may be any atom or atoms that do not adversely interfere with the nitrogen inserting into the above-described carbon hydrogen bonds.
(i) xe2x80x9cCarbene groupxe2x80x9d refers to a compound having a structure
Rxe2x80x94Cxe2x80x94Rxe2x80x2
where C is carbon capable of reacting with a polymer chain by inserting into the carbon hydrogen bonds of CH, CH2 or CH3 groups, both aliphatic and/or aromatic, of a polymer chain. It is believed that the carbon most preferred for inserting into the carbon hydrogen bonds has one lone pair of electrons. R and Rxe2x80x2 are independently any atom or atoms that do not adversely interfere with the carbon inserting into the above-described carbon hydrogen bonds.
j) xe2x80x9cDPO-BSAxe2x80x9d refers to the following compound:
4,4xe2x80x2-Oxydibenzenesulfonyl azide.
It has been surprisingly discovered that, an antioxidant and a coupling agent (or modifying agent) may be blended together to form a molecular melt, and that the formation of this molecular melt can phlagmatize the coupling and/or modifying agent.
In a first aspect of the invention, a molecular melt composition is disclosed comprising: (a) an antioxidant; and (b) a coupling agent.
In a second aspect of the invention, a molecular melt composition is disclosed comprising: (a) an antioxidant; and (b) a modifying agent.
In a third aspect of the invention, a method for phlagmatizing a coupling agent contained in a liquid is disclosed comprising the step of: introducing an antioxidant into the liquid. The coupling agent, which preferably is a poly(sulfonyl azide), may be dissolved or suspended in the liquid; and the antioxidant may be introduced before or after the coupling agent is produced.
In a fourth aspect of the invention, a method for phlagmatizing a modifying agent contained in a liquid is disclosed comprising the step of: introducing an antioxidant into the liquid. The modifying agent may be dissolved or suspended in the liquid. The antioxidant may be introduced before or after the coupling agent is produced.
In a fifth aspect of the invention, a method for making a molecular melt is disclosed comprising the steps of: introducing an antioxidant into a liquid containing a coupling agent and recovering the molecular melt. If it is desired to recover the molecular melt in a dry form, it can be recovered by precipitation from the liquid, or alternatively, the molecular melt may be recovered by co-crystallizing the antioxidant and the coupling agent.
In a sixth aspect of the invention, a method is disclosed for making a coupled polymer comprising the steps of mixing a molecular melt with a polymer; and reacting the molecular melt with the polymer. Preferably, the polymer is a polyolefin, more preferably a propylene based polymer and the coupling agent is preferably a poly(sulfonyl azide). The reaction typically will take place in a polymer extruder, which will both mix the molecular melt and the polymer and provide the energy necessary to cause the reaction between the molecular melt and the target polymer.
Additionally, it has been surprisingly discovered that, when the coupling agent (or modifying agent) is formed into a molecular melt, the efficiency of the coupling agent for modifying the polymer may be increased. Therefore, another aspect of the invention is the use of molecular melt to provide a more efficient method for making modified polymers and the compositions that result from such methods. Depending on the process used, the modifying agent used, the coupling agent used, and the concentrations of the coupling agents and/or modifying agents, this can provide rheology modified polymers, functionalized polymers, and/or cross-linked polymers (including, but not limited to thermosets).
It is believed that the molecular melt will greatly ease the manufacture of coupling and modifying agents to be used for polymers. It is also believed that the polymer modification processes that use such molecular melts will be far superior in efficiency and cost effectiveness than previously described processes.